Light filter for improving vision

ABSTRACT

A light filter for filtering light for a human eye with the filter being formed of a plastic material in combination with the filtering material. The filtering material is added so as to provide the filter with spectral transmittance characteristics which include a cut-off location (λH) of 450 nm to 550 nm, a steepness (S) for the transmittance curve at the cut-off location of at least 1%.nm -1 , a means transmittance (τ 2 ) in a spectral range from 380 to 450 nm of at most 20%, and a means transmittance (τ 3 ) in a spectral range from 450 to 550 nm of at least 40%. The filtering material preferably includes an organic dye dissolved in the plastic or an organic pigment finely distributed in the plastic material. In addition, the mean transmittance (τ 2 ) in the 380 to 450 nm spectral range is at most 10% and the means transmittance (τ 3 ) in the 450 to 550 nm spectral range is at least 60%. Further, the light filter has a means transmittance of (τ 4 ) in a 550 to 780 nm spectral range of at least 65% and a means transmittance (τ 1 ) in a 250 to 380 nm spectral range of at most 10%.

TECHNICAL FIELD

The present invention relates to a light filter, which is either locatedin the region of the eye or that filters the light before it reaches thevisual field.

INDUSTRIAL APPLICABILITY

Among many people, particularly older persons, the cornea and lens ofthe eyes are subject to disturbances with reference to the lighttransmission. These disturbances, which are frequently referred to ascataracts, result in the scattering of light incident on the eye and ininherent fluorescence. These effects appearing in the lens causedazzling and swamping phenomena which lead to a reduction of visualacuity and the contrast vision. The short-wave spectral range of thelight is scattered considerably more than the longer-wave range,furthermore it causes the fluorescence in the lens. In addition to this,the short-wave spectral portion also impairs the vision of people withretina-related weakness of vision.

PRIOR ART

Hitherto, this pathological change in the eye, also referred to as greycataracts, has been treated surgically. In this operation, the lens isremoved surgically and the missing lens is, in an older method,compensated for by cataract lenses. The glasses of these cataract lensescomprise a high diopter rating, are thick, heavy and disfigure theappearance of the wearer considerably due to the great distortions.

A modern method is to implant a lens made of plastic to replace theremoved natural lens. Here, too, as with the cataract lenses, the eyecan no longer accommodate, that is to say adjust itself sharp to thedifferent distances of the viewed object. In addition to theconsiderable physiological and psychological discomfort, the lack ofaccommodation impairs strongly also the viewing ease as compared withpeople with normal eyesight.

DESCRIPTION OF THE INVENTION

It is the object of the present invention to provide a light filterwhich postpones the otherwise necessary eye operations or even rendersthem superfluous.

The invention makes it possible for people suffering from weakness ofvision to see better by improving the visual acuity and the contrastvision, respectively. There are a lot of people who are almost blindbecause of different eye infirmities and visual error, and whoseweakness of vision is based on the loss of the visual acuity and thecontrast vision, respectively.

The invention provides essential advantages for people with healthy eyestoo. So the psychological essential effect of continuous sun shiningshall be given and the colour contrast and the stereoscopic vision shallbe improved. The vision conditions shall be improved in fog, rain or ina snow-storm. These positive effects in particular are advantageous forpeople driving motor vehicles, guiding boats or flying aircraft and forparticipation in and view of fast sports.

On one hand it is decisive, that the spectral portion of the radiationwith a wave length smaller than 450 nm (ultraviolet, violet, blue) isfiltered out totally or at least partly, before the radiation enters theeye. On the other hand a greater radiation portion, the wave length ofwhich is above 450 nm, must enter the eye and reach the retina todeliver enough information for good viewing ease.

The practical solution of this problem is achieved basically by twodifferent methods:

1. The radiation is filtered directly before it enters the eye.

2. The radiation is filtered before entering the visual field.

In the first case, the filtering takes place in a contact lens, a pairof spectacles or in a clip-on lens attached to the spectacles.

In the second case, the daylight entering the room is filtered in thearea of the entrance place (e.g. window, skylight, door glazing). In thecase of artificial room lighting, the light is filtered in the area ofthe lamp. In the case of TV sets, monitors, etc. the filtering of theemitted light can take place in front of or on the screen. Filtering canbe effected in this cases among others by placing a light filter infront of the light source in the form of a foil, pane or housing, or inthe form of lacquer or interference coatings.

This problem is solved according to the invention in such a way, that bymeans of the light filter the visual acuity and the contrast vision willbe improved through its mean transmittance which, in the 380 to 450 nm(τ₂) spectral range, is at most 20%, preferably at most 10% and stillmore preferably at most 1% and, in the 450 to 550 nm (τ₃) spectralrange, is at least 40%, preferably at least 60% and still morepreferably at least 70%.

Detailed ophthalmological investigations have shown that a markedimprovement of eye sight was detected among patients using the lightfilter, particularly in the low-contrast range. This improvement wassignificant and reproducible with regard to visual acuity and contrastvision. In addition to this, the psychologically positive impression ofpermanent sunshine was achieved by filtering out the blue and blue-greenspectral portions. This latter effect is to be attributed to the yellowcolor of the light filter.

On the other hand, the extensive investigations on which the inventionis based showed that a higher mean transmittance is necessary in the 550to 780 nm spectral range in order to provide the retina with sufficientinformation for color vision. This applies above all for inside roomsand at night.

According to the invention, the light filter's mean transmittance in the550 to 780 nm (τ₄) spectral range is therefore at least 45%, preferablyat least 65% and still more preferably at least 85%.

Further investigations showed that the spectral portion of 250 to 380 nmwhich is in the ultraviolet range should be kept away from the eye inorder to reduce the risk of damage in the conjunctiva, cornea and lens.

According to the invention, the light filter's mean transmittance in the250 to 380 nm (τ₁) spectral range is thus at most 10%, preferably atmost 1% and still more preferably at most 0.1%.

A further result of the investigations was that, with regard to viewingease, the light transmittance values of the light filter are linked tothose of the mean transmittance in the 450 to 550 nm spectral range.

Hence it follows, according to the invention, that the meantransmittance in the 450 to 550 nm (τ₃) range is at least 0.6 times asmuch, preferably at least 0.7 times as much and still more preferably atleast 0.8 as much as the light transmittance (τ_(vis)).

The aforementioned investigations showed furthermore that the cut-offlocation (λ_(H)) of the light filter must be within a relatively narrowspectral range of about 450 to 550 nm in order to achieve optimumeffects. The cut-off location is that point on the spectraltransmittance curve rising to the long-wave range at which half of themaximum transmittance in the 380 to 780 nm range is registered.

Hence it follows according to the invention that the cut-off location(λ_(H)) is at least 450 nm and at most 550 nm.

The investigations showed that, in addition to the cut-off location(λ_(H)), the steepness of the transmittance curve (S) plays also asubstantial role. A too plateaued rise of the transmittance curve wouldconsiderably impair the desired effect.

Hence it follows according to the invention that the steepness of thetransmittance curve (S) at the wavelength of the cut-off location is atleast 1% . nm⁻¹, preferably at least 2% . nm⁻¹ and still more preferablyat least 3% . nm⁻¹.

The spectral transmittance properties (τ(λ)) of the light filter aredetermined by the spectral properties of the base material and filtermaterial distributed therein.

For practical use in the region of the eye, the light filter can bedesigned as a contact lens or as a spectacle or clip-on lens. If it isdesigned as a contact lens made of plastic, then the filter material isincorporated in the base material and homogenously distributed therein.The same applies to spectacle or clip-on lenses which are made either ofplastic or of glass.

It is thus a further feature of the invention that the filter materialis incorporated in the base material of the contact lens or spectacle orclip-on lens during production to be homogeneously distributed thereafter production. If glass is used for the spectacle or clip-on lenses,yellow filter glass can be utilized.

Thus, according to an embodiment of the invention yellow colored glassis utilized, if glass as spectacle or clip-on lens is used.

In some cases, it is possible that the light filter has not a constantthickness across its entire surface. This will above all be the case atcontact lenses and spectacle lenses used for correction. If the filtermaterial is homogeneously distributed in the base material, then thespectral transmittance is not identical across the entire surface due todeviations in the thickness. In order to offset this disadvantage, alayer with constant thickness and homogeneous surface concentration withrespect to the filter material is embedded in the interior or appliedexternally. Embedding this filter layer in the interior can be achievedin different ways. For instance, the filter layer can be laminated withthe cover layers. It is also possible to build up the cover layers andthe filter layer in a casting process or by multi-layer extrusion.Further the filter layer can be applied as a cover coating in the formof lacquer and the opposite one can be applied as a second covercoating.

A further embodiment of the invention thus arises, if the light filteris embedded in the interior or applied externally as a layer withconstant thickness during the production of the contact lens and of thespectacle lens respectively.

The practical tests revealed that an elegant method is to ink thecontact lens or spectacle lens subsequently with the color filter. Thiscan be done with a lacquer in which the filter material is homogeneouslydistributed and which adheres well to the material of the contact lensresp. of the spectacle lens. For instance, lacquers on the base ofpolyvinyl chloride, acryl, epoxy, polyurethane, polyester and fluorinepolymer have proved to be favorable.

The light filter may be a lacquer layer for the purpose according to theinvention.

In practice, it has proved advantageous for the lacquer layer to belargely scratch-proof. Siloxane lacquer either containing the filtermaterial or applied as an additional cover coating without specificfiltering properties is highly suitable for this purpose.

Within the scope of the invention, the largely scratch-proof lacquerlayer may be applied as siloxane lacquer in which the filter material ishomogeneously distributed or as an additional cover coating withoutspecific filtering properties.

The large degree of scratch-proofness can also be achieved byevaporating transparent layers (e.g. quartz, glass, metal oxides, etc.).In this way, the light filter can also be evaporated using suitablematerials. A further possibility for applying the light filter is byapplying the interference layers in baths.

If the light filter is manufactured in the form of a contact lens inwhich the filter material reaches up to the surface, the filter materialmay be dissolved by lachrymal fluid, and may irritate or even damage theeye. The investigations showed that, in this case, it is expedient toapply a cover coating which prevents the filter material from beingdissolved out.

In this embodiment of the invention, in the case of a contact lens, anadditional layer which protects the eye is applied externally.

In those cases where the light filter is e.g. not supposed to becontinuously worn in connection with a pair of spectacles, the lightfilter may also be designed as a clip-on lens. This is a slip-onattachment which even can have a turn-up design.

Thus the invention comprises, as a further variant, a light filter whichis designed as a rigid, removable and/or turn-up attachment forspectacles.

In order to avoid breakage of the spectacles or clip-on lens, it may bemade of a material with increased impact strength. Suitable for thisare, for instance, polycarbonate, cellulose-ester and acryl glass withincreased impact resistance, which all have the advantage of beinglight-weight, and highly transparent duroplasts such as CR 39, which isnamed as being representative for the whole group of materials.

According to a further embodiment of the present invention the materialfrom which the spectacles or clip-on lenses are made has an impactstrength of at least 15 kJ . m⁻², preferably at least 40 kJ . m⁻², stillmore preferably at least 65 kJ . m⁻².

If the light filter is made of glass, it is expedient to modify theoptical base glass (silicate glass) by adding metals or metal compoundsand to admix cadmium sulfide which is distributed colloidally by meansof the tarnishing process.

If the light filter is made of plastic, then soluble organic dyes andorganic or inorganic pigments of the smallest particle sizes aresuitable as filter materials.

The following soluble organic dyes have proved to be suitable: styryl,quinophthalone, naphthazine, pyrazolone, mono- and diazo derivatives.

The following are suitable pigments: quinacridones, isoindolinones withor without cobalt complexes resp. copper complexes, aryl amides,diarylides and lead/(sulfur)/chromium compounds.

If the soluble dyes or pigments do not sufficiently filter out theultraviolet spectral portion, then it is recommended to usebenzotriazoles or benzophenones as additional filter materials.

BRIEF DESCRIPTION OF THE DRAWINGS Some embodiments of the invention areillustrated in the drawings:

FIG. 1 shows the spectral transmittance degree of a light filteraccording to the invention made of glass.

FIG. 2 shows the spectral transmittance degree of a light filteraccording to the invention made of plastic.

THE BEST WAY TO CARRY OUT THE INVENTION

The spectral transmittance degree (τ(λ)) represented in FIG. 1 shows thepermeability of the light filter as a function of the wavelength. Thelight filter is a 2 mm thick yellow colored glass pane whose compositionand properties are described in example 1.

The spectral transmittance degree (τ(λ)) shown in FIG. 2 applies to 2 mmthick light filter made of polycarbonate whose composition andproperties are described in example 2.

EXAMPLE 1

The light filter is a yellow colored glass pane with a thickness of 2mm. It consists of a silicate basis glass melt into which 10% filtermaterial as admixture SEEMORE YELLOW G 01 (MutzhasProduktions-Gesellschaft mbH, Munich) is added. The curve (τ(λ) is shownin FIG. 1. The following individual values are obtained:

τ₁ <1%

τ₂ <1%

τ₃ =76%

τ₄ =91%

τ_(vis) =88%

τ₃ 1τ_(vis) =0.86

λ_(H) =465 nm

S=3.1% . nm⁻¹

EXAMPLE 2

The light filter is a pane made of 2 mm thick polycarbonate. Prior tothe injection molding, 5% filter material were added to the PC granulesin the form of a SEEMORE YELLOW PO 1 master batch (MutzhasProduktions-Gesellschaft mbH, Munich). The curve (τ(λ) is shown in FIG.2. The following individual values were obtained:

τ₁ <1%

τ₂ <1%

τ₃ =63%

τ₄ =89%

τ_(vis) =89%

τ₃ τ_(vis) =0.74

λ_(H) =475 nm

S=2.8% . nm⁻¹

The impact strength of this light filter exceeds 65 kJ . m⁻².

Not only spectacles or clip-on lenses can be produced in this way, butalso covers for inside room lights. In the latter case spectacles orcontact lenses with light filters need not be worn in this room when theartificial lighting is on.

EXAMPLE 3

Two colorless acrylic glass panes (PMMA) are held in a frame at mutualdistance of 1 mm. Methyl methacrylate containing 9% filter materialSEEMORE YELLOW PO 2 (mutzhas Produktions-Gesellschaft mbH, Munich) ispoured into the interspaces and subsequently polymerized. Spectaclelenses for corrective spectacles can then be made from this sandwich.The following individual values are obtained:

τ₁ <0.1%

τ₂ <0.2%

τ₃ =70%

τ₄ =91%

τ_(vis) =86%

τ₃ τ_(vis) =0.81

λ_(H) =470 nm

S=2.9% . nm⁻¹

Soft and hard contact lenses can be manufactured in similar way usingthe known polymers, whereby the admixture materials SEEMORE YELLOW PO3,PO4, PO5 or PO6 (Mutzhas Produktions-Gesellschaft mdH, Munich) are used.

EXAMPLE 4

Spectacle lenses for corrective spectacles are dipped into a lacquer inwhich 14% filter material SEEMORE YELLOW PO7 is dissolved. The followingvalues are obtained after drying:

τ₁ <0.1%

τ₂ <1%

τ₃ =65%

τ₄ =85%

τ_(vis) =88%

τ₃ 1τ_(vis) =0.76

λ_(H) =475 nm

S=2.7% . nm⁻¹

EXAMPLE 5

12% filter material SEEMORE YELLOW PO8 (Mutzhas Produktions-GesellschaftmbH, Munich) are worked into the base material of the contact lens.After completion, the contact lens is coated with a protective layer ofbase material by injection molding or dipping. The following values areobtained:

τ₁ <1%

τ₂ <2%

τ₃ =64%

τ₄ =89%

τ_(vis) =85%

τ₃ 1τ_(vis) =0.75

λ_(H) =475 nm

S=2.7% . nm⁻¹

EXAMPLE 6

6% filter material SEEMORE YELLOW PO9 (Mutzhas Produktions-GesellschaftmbH, Munich) are worked into the base material of a PVC film. Thefollowing values are obtained:

τ₁ <1%

τ₂ <1%

τ₃ =59%

τ_(vis) =85%

τ₃ 1τ_(vis) =0.73

λ_(H) =480 nm

S=2.7% . nm⁻¹

This film filters the daylight coming in through the window panes, sothat there is no need to wear a pair of spectacles or contact lenseswith light filters in this room in daylight.

EXAMPLE 7

A 3 mm thick extruded acryl glass pane contains 3% SEEMORE YELLOW PO10(Mutzhas Produktions-Gesellschaft mbH, Munich) filter material. Thefollowing individual values are obtained:

τ₁ <0.1%

τ₂ <0.2%

τ₃ =70%

τ₄ =91%

τ_(vis) =86%

τ₃ 1τ_(vis) =0.81

λ_(H) =470 nm

S=2.9% . nm⁻¹

If the picture tube of a color TV set is covered with this light filter,than it is possible to watch TV without having to wear spectacles orcontact lenses with light filters.

EXAMPLE 8

The light filter are sun glasses, the panes of which consisting ofpolycarbonate (see example 2). Additionally 3% of a neutral filtermaterial as masterbatch SEEMORE GRAY P01 (MutzhasProduktions-Gesellschaft mbH, Munich) is mixed into the PC granulate.The following individual values are obtained:

τ₁ <0,02%

τ₂ <1%

τ₃ =14%

τ₄ =20%

τ_(vis) =19%

τ₃ 1τ_(vis) =0,74

λ_(H) =475 nm

S=2,8% . nm⁻¹

Here it is essential that τ₃ is at least five times, preferably at least10 times and furtheron preferably at least 50 times of τ₂. Furthermore,the following criteria should be fulfilled:

a) The mean transmittance of the light filter in the 250 to 380 nmspectral range is at most 10%, preferably at most 1% and still morepreferably 0.1%;

b) The mean transmittance of the light filter in the 450 to 550 nm rangeis at least 0.6 times as much, preferably at least 0.7 times as much andstill more preferably at least 0.84 times as much of the lighttransmittance (τ_(vis));

c) The cut-off location (λH) of the filter is at least 450 nm and atmost 550 nm; and

d) The steepness (S) of the transmittance curve of the cut-off location(λH) of the filter is at least 1%.nm⁻¹ preferably at least 2%.nm⁻¹ or,more preferably, at least 3%.nm⁻¹. This is valid also with regard to therecognizing of traffic signal colors. The neutral filter materialtransmits within the wave length range of 96₄ largely independent fromthe wave length, nearly constant.

EXAMPLE 9

The light filter are sun spectacles the panes of which consisting ofpolycarbonate. Before injection moulding 5% filter material asmasterbatch SEEMORE GREEN PO1 (Mutzhas Produktions-Gesellschaft mbH,Munich) is admixed to the PC-granulate. The following individual valuesare obtained:

τ₁ <0.1%

τ₂ <1%

τ₃ =42%

τ₄ =60%

τ_(vis) =53%

τ₃ 1τ_(vis) =0.79

λ_(H) =475 nm

S=1.8% . nm⁻¹

When the light filter described in example 2 was used, the followingchanges of visual acuity (SNELLEN ACUITY) were detected in tests withelderly test persons being measured in a distance of 20 feet (6.1 m)from the visual object.

    ______________________________________                                        Contrast    without light filter                                                                       with light filter                                    ______________________________________                                         3%         20/180       20/99                                                10%         20/65        20/49                                                ______________________________________                                    

EXAMPLE 10

The light filter is a sheet of polycarbonate with a thickness of 2 mm.Before injection moulding a bit less than 5% of the filter material asmasterbatch SEEMORE YELLOW P01 (Mutzhas Produktions-Gesellschaft mbH,Munich) is admixed to the PC-granulate. After the injection moulding thesheet is coated with siloxane lacquer. The following individual valuesare obtained:

τ₁ <0.1%

τ₂ <1%

τ₃ =63%

τ₄ =91%

τ_(vis) =90%

τ₃ 1τ_(vis) =86

λ_(H) =476 nm

S=2.6% . nm⁻¹

EXAMPLE 11

If the light filter according to example 10 is made non-reflective atboth sides by vapour-deposition, than the following values are achieved:

τ₁ <0.1%

τ₂ <1%

τ₃ =64%

τ₄ =96%

τ_(vis) =92%

τ₃ 1τ_(vis) =0.70

λ_(H) =476 nm

S=2.6% . nm⁻¹

Accordingly, it has been possible for the first time to produce suchspectacles according to DIN 58216 and DIN 58Z17 for the drivers of avehicle which meet these requirements at the day, at the night and intwilight. Required is τ_(vis) >80% (according to remark in DIN 58216τ_(vis) >85%). The relative weakening quotients for the signal lightsred Q_(RED), yellow Q_(YELLOW), green Q_(GREEN) and blue Q_(BLUE) mustbe ≧0.8. The following values are reached.

Q_(RED) =0.95

Q_(YELLOW) =0.97

Q_(GREEN) =0.90

Q_(BLUE) =0.80

EXAMPLE 12

The light filter is a polycarbonate sheet with a thickness of 2 mm.Before injection moulding closely 2.5% filter material as MasterbatchSEEMORE YELLOW P01 (Mutzhas Produktions-Gesellschaft mbH, Munich) isadmixed to the PC-granulate. After the injection moulding the sheet iscoated with siloxane lacquer. The following individual values areobtained:

τ₁ <0.1%

τ₂ <2%

τ₃ =66%

τ₄ =90%

τ_(vis) =87%

τ₃ 1τ_(vis) =0.76

λ_(H) =468 nm

S=2.6% . nm⁻¹

Q_(RED) =0.89

Q_(YELLOW) =0.92

Q_(GREEN) 0.84

Q_(BLUE) =0.80

EXAMPLE 13

The light filter is a sheet of polymerized allyl-diethylen glycolcarbonate (ADC) with a thickness of 2 mm. Before polymerizing 5% filtermaterial SEEMORE YELLOW P11. (Mutzhas Produktions-Gesellschaft mbH,Munich) is admixed to the monomer. The following individual values areobtained:

τ₁ <0.1%

τ₂ <1%

τ₃ =64%

τ₄ =92%

τ_(vis) =87%

τ₃ 1τ_(vis) =0.74

λ_(H) =476 nm

S=2.6% . nm⁻¹

Q_(RED) =0.90

Q_(YELLOW) =0.92

Q_(GREEN) 0.85

Q_(BLUE) =0.80

EXAMPLE 14

If the light filter according to example 13 is made non-reflective atboth sides by vapour-deposition, than the following values are achieved:

τ₁ <0.1%

τ₂ <1%

τ₃ =64%

τ₄ =99%

τ_(vis) =93%

τ₃ 1τ_(vis) =0.65

λ_(H) =476 nm

S=2.6% . nm⁻¹

Q_(RED) =0.96

Q_(YELLOW) =0.98

Q_(GREEN) 0.91

Q_(BLUE) =0.81

SUMMARY OF THE FORMULA SYMBOLS

τ(λ): Spectral transmittance degree of the light filter

τ₁ : Mean transmittance of the light filter from 250 to 380 nm

τ₂ : Mean transmittance of the light filter from 380 to 450 nm

τ₃ : Mean transmittance of the light filter from 450 to 550 nm

τ₄ : Mean transmittance of the light filter from 550 to 780 nm

τ_(vis) :Light transmittance of the light filter from 380 to 780 nmrelative to light type D 65

λ_(H) : Cut-off location (nm) point on the spectral transmittance curverising to long-wave range at which half of the maximum transmittance inthe 380 to 780 nm range is registered (nm)

S: Edge steepness (% . nm⁻¹), steepness of the spectral transmittancecurve at point λ_(H)

The addmixtures or masterbatches respectively contain the followingcomponents the face concentration thereof in the finished light filterbeing given in parentheses.

Seemore Yellow G01:

Sulfur- (0.01-10 g/m²) and/or Cadmiumsulfide (0.01-10 g/m²) SeemoreYellow P 01 to P11, Seemore Gray P 01 and Seemore Green P01:

As UV-absorbers benzotriazoles (0.1-50 g/m²) and/or benzophenones(0.1-50 g/m²) as well as soluble coloring substances and/or colorpigments of the color material groups antrachinon (0.1-5 g/m²),chinakridon (0.1-5 g/m²), diazo (0.1-5 g/m²), monoazo (0.1-5 g/m²),phtalocyanin (0.1-5 g/m²), pyrazolon (0.1-5 g/m²), black (0.1-5 g/m²).the color substances can be used alone or in combination.

An UV-absorber concentration of 2-5 g/m² and a coloring substanceconcentration of 0.1-0.3 g/m² is proved to be particularly advantageous.

We claim:
 1. A light filter for filtering light for a human eye, saidfilter being formed of plastic material combined with a filteringmaterial so as to provide said filter with the following transmittancecharacteristics:a) a cut-off location (λH) of 450 nm to 550 nm, whereinthe cut-off location is that point on a spectral transmittance curve forthe filter at which half of a maximum transmittance in a 380 to 780 nmrange is registered, b) a steepness (S) for the transmittance curve atthe cut-off location of at least 1%nm⁻¹, c) a means transmittance (τ₂)in a spectral range from 380 to 450 nm of at most 20%, and d) a meanstransmittance (τ₃) in a spectral range from 450 to 550 nm of at least40%.
 2. A light filter according to claim 1 wherein said filteringmaterial includes an organic dye dissolved in the plastic materialforming said filter.
 3. A light filter according to claim 1 wherein saidfiltering material includes an organic pigment finely distributed in theplastic material forming said filter.
 4. A light filter according toclaim 1 wherein the mean transmittance (τ₂) in the 380 to 450 nmspectral range is at most 10% and the mean transmittance (τ₃) in the 450to 550 nm spectral range is at least 60%.
 5. A light filter according toclaim 1 wherein the means transmittance (τ₂) in the 380 to 450 nmspectral range is at most 1% and the mean transmittance (τ₃) in the 450to 550 nm spectral range is at least 70%.
 6. A light filter according toclaim 1 wherein said filter has a mean transmittance (τ₄) in a 550 to780 nm spectral range of at least 45%.
 7. A light filter according toclaim 1 wherein said filter has a mean transmittance (τ₄) in a 550 to780 nm spectral range of at least 65%.
 8. A light filter according toclaim 1 wherein said filter has a mean transmittance (τ₄) in a 550 to780 nm spectral range of at least 85%.
 9. A light filter according toclaim 1 wherein said filter has a mean transmittance (τ₁) in a 250 to380 nm spectral range of at most 10%.
 10. A light filter according toclaim 1 wherein said filter has a mean transmittance (τ₁) in a 250 to380 nm spectral range of at most 1%.
 11. A light filter according toclaim 1 wherein said filter has a mean transmittance (τ₁) in a 250 to380 nm spectral range of at most 0.1%.
 12. A light filter according toclaim 1 wherein said light filter has a means transmittance (τ₃) in the450 to 550 nm range of at least 0.6 times as much as a lighttransmittance value (τ_(vis)) of said filter is a spectral rang of 380to 780 nm.
 13. A light filter according to claim 1 wherein said lightfilter has a means transmittance (τ₃) in the 450 to 550 nm range of atleast 0.7 times as much as a light transmittance value (τ_(vis)) of saidfilter is a spectral rang of 380 to 780 nm.
 14. A light filter accordingto claim 1 wherein said light filter has a means transmittance (τ₃) inthe 450 to 550 nm range of at least 0.8 times as much as a lighttransmittance value (τ_(vis)) of said filter is a spectral rang of 380to 780 nm.
 15. A light filter according to claim 1 wherein the steepness(S) of the transmittance curve at the cut-off location (λH) is at least2%.nm⁻¹.
 16. A light filter according to claim 1 wherein the steepness(S) of the transmittance curve at the cut-off location (λH) is at least3%.nm⁻¹.
 17. A light filter according to claim 1 wherein said plasticmaterial has an impact resistance of at least 15 KJ.m⁻².
 18. A lightfilter according to claim 1 wherein said plastic material has an impactresistance of at least 40 KJ.m⁻².
 19. A light filter according to claim1 wherein said plastic material has an impact resistance of at least 65KH.m⁻².
 20. A light filter according to claim 3 wherein said pigmentconcentration is 0.1 to 5 g/m².